Overhead electric power transmission and distribution systems typically comprise multiple lines of conductors that are supported above the ground by support towers. Support towers can also be referred to as transmission towers, poles or pylons. The multiple lines of conductors also referred to simply as conductors, can form one or more circuits. The conductors are connected to the support towers by insulators, for example ceramic insulators.
Conductors can carry multiple hundreds of kilowatts. Overhead electric power transmission and distribution systems often utilize air as a primary conductor insulator. In other words, the conductors themselves can be highly energized but without any insulating material. The support towers are designed to avoid having the energized conductors arching, or directly contacting other structures and other conductors.
In order to conduct greater current loads, multiple conductors can be arranged in a parallel bundle. Conductors are bundled to each other by spacer dampers that are positioned along the length of the bundled conductors to ensure adequate spacing between individual conductors. Spacer dampers are also referred to as spacers. Bundled conductors are widely used because, in addition to conducting high current loads, this arrangement can provide a number of other benefits such as: improved thermal dissipation, increased ampere capacity and decreased corona loss.
Overhead electric power transmission and distribution lines can be exposed to harsh conditions, such as high winds, earthquakes, snow and ice. In light of these conditions, the support towers and the spacers must maintain sufficient clearance between the conductors, other structures and the ground. The requirement of sufficient clearance necessitates regular inspection and maintenance of support towers and the conductors by specialized workers or linemen, who ride in so-called line carts, which are carried on the conductors.
Cranes or helicopters can be used to place the line carts upon the conductors and to advance the line carts past the insulators on support towers. The line carts are also referred to as conductor carts and maintenance carts or skips. The line carts are designed to support and transport a worker, typically referred to as lineman or lineperson, along sections of the conductors. The line carts must be able to support the weight of the worker, their tools, and replacement equipment, such as replacement spacers, while moving the lineperson along the conductors.
U.S. Pat. No. 8,794,380 to Glenn, J. R. et al. (Glenn) teaches a line cart. The Glenn line cart is self-propelled and it includes a gasoline engine, a gasoline tank, a hydraulic pump, a hydraulic tank and hydraulic motors to drive rollers that contact two bundled conductors. Glenn teaches the use of positive engagement rollers that contact the opposite surface of the conductor lines to force the conductor lines against the drive rollers to improve the drive rollers traction. Glenn also teaches a non-motorized trolley that is pulled along the conductors by a winch. The trolley includes one or more mechanically actuated disc brakes. The various components of the Glenn line cart necessitate the use of a helicopter or crane truck to advance the line cart past the support insulators on support towers.